The present invention relates to disc recorders and more specifically to recorders in which video information is recorded on a rapidly rotating magnetic disc. The disc used in such a recorder may be constructed of either rigid or flexible material. The recording disc is rapidly rotated and one or more transducer heads are positioned adjacent the recording surface to record and reproduce the video information. If desired, transducers may be provided for recording and playback on both sides of the recording disc.
Recording of video signals on a disc recorder may be accomplished in a number of ways. In one format, the video signal is stored in a number of circular concentric recording tracks and the transducer is moved only intermittently to the desired track for recording or playback. Generally one field of video information will be stored in each of the tracks. The disc will be rotated, therefore, at a rate equivalent to the field rate of the video signal.
A second recording format for disc recorders is shown in U.S. Pat. No. 3,509,274, to Kihara, issued on Apr. 28, 1970. The transducer head is moved radially during disc rotation such that a continuous spiral track is defined. While such a recording format permits a slower transport mechanism to be utilized, this format is disadvantageous in that continuous high quality reproduction of a single video field, or series of fields, is not easily obtained.
Regardless of the format used, however, it is clear that a controlled, dimensionally precise transport must be provided for each transducer. One type of prior art transducer transport is shown in U.S. Pat. No. 3,770,905 to Sperry, issued Nov. 6, 1973, and U.S. Pat. No. 3,814,441 to Craggs, issued June 4, 1974. These patents show transport mechanisms in which a radially disposed, threaded rod engages the transducer carriage and is rotated by a stepping motor to move the transducer radially with respect to the disc. Since the carriage mechanism and the threaded rod it engages are both moving, the inertia of the transport is significant and a rapid stepping motion is difficult to obtain.
A second type of prior art transducer transport mechanism is shown in U.S. Pat. No. 3,539,716, issued Nov. 10, 1970, to Stratton et al. In this type of transport mechanism, a transducer carriage is moved radially by means of a carriage belt. The belt forms a loop around an idler pulley which is adjacent the center of the recording disc. Both ends of the belt are positively attached to the drive pulley, with each end being wrapped around the drive pulley a number of times. Positive engagement of the belt by the drive pulley is required since a frictional drive arrangement would always be subject to slippage and the resulting misalignment of the transducer with respect to the recording tracks. Since it is necessary to attach positively both ends of the drive belt to the drive pulley, with each end being wrapped around the drive pulley a number of times, the belt ends must be attached to the drive pulley at different levels. As shown in the Stratton et al patent, the idler pulley must therefore be skewed with respect to the drive pulley to compensate for the fact that the drive belt must change levels as it extends around the idler pulley. An arrangement of this type is somewhat disadvantageous in that there will always be a certain amount of friction between the drive belt and the idler pulley. Additionally, each section of the drive belt extending from the idler pulley to the drive pulley will be twisted along its length and will exert in undesirable torque on the transducer carriage.